Hunter College, CUNY - CHEMISTRY 222Chap 16 Pi Systems F18 HW KEY

Org II (Hamann) Chapter 17 HW – Pi Systems Name 1 Draw the structures of the following compounds a) cyclopentadiene (explain why the numbers for the double bonds (1,3-), which are formally require d, are usually omitted. I.e., why is only one isomer possible; why not 1,2- or 1,4-cyclopentadiene? 1,2-cyclopentadiene would contain an allene, a linear C=C=C unit that would make the ring too strained. 1,4- cyclopentadiene would actually be the same molecule, but numbered incorrectly. Hence the use of the numberless name. b) 1,3,5-cycloheptadiene c) (2E, 4Z)-2,4-heptadiene d) isoprene , ocassionally referred to as 2-methyl-1,3-butadiene 2 Draw a molecule that has the following characteristics. a) a decalin with both conjugated and non-conjugated double bond (three double bond total) (Numerous other possibilities) b) a compound containing a 5-member ring and conjugated doubles bond that are locked in an s-trans orientation c) an eight-member ring containing two cumulated double bonds (i.e., an allene) highly strained d) a decalin with two double bonds that are locked in an s-cis orientation (numerous other possibilities) 3 a) Draw isoprene in both the s-cis and the s-trans confirmation conjugated non-conjugated to other two HC